The severity of the HIV epidemic and limits on prevention and treatment resources have forced planners and providers to make difficult choices about which interventions to implement to prevent and treat HIV and substance abuse. The goal of our project is to evaluate existing and potential HIV and substance abuse interventions to provide critical information on effectiveness, public-health impact, and efficiency. This project aims to promote reasoned planning and policy making in the realm of HIV and substance abuse prevention and treatment via the development of mathematical and economic models. To achieve this goal, we have the following specific aims: 1. To estimate production functions that characterize the relationship between program expenditures and health outcomes, such as reductions in risky behaviors for prevention programs and delivery of services for treatment programs 2. To develop model-based methods of translating the behavioral impact of HIV-related interventions into epidemiologically meaningful outcome measures, such as years of life saved. 3. To determine how best to estimate health outcomes, economic outcomes, and cost effectiveness of HIV and substance abuse interventions. 4. To assess the effectiveness and cost-effectiveness of specific interventions aimed at preventing and treating HIV and substance abuse. 5. To inform the allocation of societal resources by examining the effectiveness and cost effectiveness of portfolios of prevention and treatment interventions. This work includes analyzing national and international HIV prevention and treatment strategies, and assessing how to balance HIV prevention and treatment interventions to achieve the greatest health benefit. 6. To examine the relationship between policy modeling and public health decision making in the areas of HIV and substance abuse - in particular, to explore how to make analyses most useful to policy makers. The proposed research will advance the state of the art in HIV planning and policy modeling, critically evaluate promising interventions, and help provide the scientific foundation for allocation of scarce resources to portfolios of HIV and substance abuse prevention and treatment interventions.